Structural aspects of magnesium deficiency

Abstract

Structural changes of cells and tissues in herbaceous agricultural plants caused by nutrient deficiencies have already been studied extensively at the levels of both light and electron microscopy, and have partially proved to be of considerable diagnostic value (Thomson and Weier, 1962; Thomson et al., 1964; Bussler, 1964, 1981; Whatley, 1971; Hecht-Buchholz, 1972, 1983; Pissarek, 1973, 1979; Bangerth, 1979). In trees, however, similar studies have been carried out only in a few cases, and, so far, the conifers especially have received little attention. There has been some limited research on the effects of Ca deficiency (Davis, 1949) and B deficiency (Blaser et al., 1967; Raitio, 1979) upon the structure of needles, stems, and roots of Pinus spp. and Thuja spp. Recent interest in the general effects of mineral deficiencies upon the structure and function of conifers (especially Picea abies and Pinus silvestris) arose with the occurrence of ‘New-Type Forest Decline’, which proved to be associated in many instances with Mg deficiency at high elevations on acid soils (Type I Spruce Decline; FBW, 1986; Roberts et al., 1989) or, to a lesser extent, K deficiency on calcareous soils (Type IV Spruce Decline; FBW, 1986). In the light of initial discussions on the causes of this damage (primarily soil changes by increased input of acidity or primarily direct effects of air pollutants upon the foliage), anatomical investigations of conifer needles subjected to either mineral deficiencies or various gaseous pollutants have proved to be a valuable tool for a differential diagnosis, if compared with structural changes found in affected needles from declining trees in the field (Fink, 1988, 1989, 1991, 1993; Holopainen and Nygren, 1989; Barsig et al., 1990; Holopainen et al., 1992).